Additive manufacturing techniques and processes generally involve the buildup of one or more materials to make a net or near net shape (NNS) object, in contrast to subtractive manufacturing methods. Though “additive manufacturing” is an industry standard term (ASTM F2792), additive manufacturing encompasses various manufacturing and prototyping techniques known under a variety of names, including freeform fabrication, 3D printing, rapid prototyping/tooling, etc. Additive manufacturing techniques are capable of fabricating complex components from a wide variety of materials. Generally, a freestanding object can be fabricated from a computer-aided design (CAD) model.
A particular type of additive manufacturing is more commonly known as 3D printing. 3D printing techniques and processes generally include forming and extruding a bead of flowable material (e.g., molten thermoplastic), applying such bead of material in a strata of layers to form a facsimile of an article, and machining such facsimile to produce an end product. Such a process is generally achieved by means of an extruder mounted on a computer numeric controlled (CNC) machine with controlled motion along at least the X, Y, and Z-axes. In some cases, the flowable material, such as, e.g., molten thermoplastic material, may be infused with a reinforcing material (e.g., strands of fiber) to enhance the material's strength. The flowable material, while generally hot and pliable, may be deposited upon a substrate (e.g., a mold), pressed down or otherwise flattened to some extent, and leveled to a consistent thickness, preferably by means of a tangentially compensated roller mechanism. The flattening process may aid in fusing a new layer of the flowable material to the previously deposited layer of the flowable material. In some instances, an oscillating plate may be used to flatten the bead of flowable material to a desired thickness, thus effecting fusion to the previously deposited layer of flowable material. The deposition process may be repeated so that each successive layer of flowable material is deposited upon an existing layer to build up and manufacture a desired component structure. When executed properly, the new layer of flowable material may be deposited at a temperature sufficient enough to allow the new layer of flowable material to melt and fuse with a previously deposited layer of flowable material, thus producing a solid part.
In the practice of the aforementioned process, it is necessary to provide a method of securing and holding the first layer of material in a fixed position, as it cools by an amount sufficient enough to allow the printing of subsequent layers. A method sometimes employed, is to provide a foundation sheet of thermoplastic material onto which the newly printed layer can bond. However, while the newly printed material becomes securely bonded to the foundation sheet, a problem frequently develops as the newly deposited material cools, and correspondingly shrinks. Since the newly deposited material is securely bonded to the already cooled and stabilized foundation sheet, the shape of the entire structure becomes distorted due to warpage as the deposited layer shrinks disproportionately relative to the foundation layer onto which it is deposited, and the resultant stress created between the two materials equilibrates. Such distortion frequently results in an unusable product. A method commonly practiced to overcome the warpage problems associated with solidly bonding to a foundation layer, is to deposit the initial layer onto a heated platen installed on the worktable, thus providing for some flexibility in the initial bond. In the practice of such method, the platen maintains the thermoplastic material at a temperature sufficient enough to prevent a substantial solid bonding to the initial layer. However, several disadvantages have been encountered in the application of that method; most notably, a lack of sufficient bonding between the platen and the printed material often results in subsequent movement of the workpiece as subsequent layers of material are applied. Another disadvantage is the substantial financial burden associated with providing a large heated platen.
In view of the forgoing, it is an object of the present disclosure to provide a low-cost method of securely fixing the first layer of a 3D printed thermoplastic part to a worktable top, and holding it securely enough for subsequent processing, while providing for a sufficient amount of flexibility and movement within the bond, to compensate for shrinkage of the workpiece during the cooling process, thus minimizing any warping of the substrate onto which it is deposited. A still further objective of the disclosure is to provide such an improved process and method without the requirement of complex and expensive devices.